Agenda #: 7.1
Meeting Date: July 15, 2025
TO: Honorable Mayor and Members of the City Council
FROM: Daniel Fox, City Manager
TITLE: AMENDMENTS TO TITLE 15 OF THE DIAMOND BAR CITY CODE TO
ADOPT THE STATE FIRE MARSHAL'S UPDATES TO THE VERY
HIGH FIRE HAZARD SEVERITY ZONES.
STRATEGIC
GOAL: Safe, Sustainable & Healthy Community
RECOMMENDATION:
A. Hear the staff presentation and receive any public testimony; B. Determine that the proposed ordinance does not constitute a project and is therefore exempt from the California Environmental Quality Act (CEQA) pursuant to CEQA Guidelines Section 15378(b); and
C. Introduce for first reading by title only, waive full reading of Ordinance No. 02 (2025), and set for public hearing, second reading and adoption at the August 5, 2025 City Council meeting:
ORDINANCE NO. 02 (2025) - AN ORDINANCE OF THE CITY COUNCIL OF
THE CITY OF DIAMOND BAR DESIGNATING VERY HIGH FIRE HAZARD
SEVERITY ZONES IN ACCORDANCE WITH STATE LAW AND AMENDING THE DIAMOND BAR CITY CODE.
FINANCIAL IMPACT:
None.
BACKGROUND:
On November 15, 2022, the City Council adopted Ordinance No. 03(2022), which incorporated the California Building Standards Code by reference pursuant to Health and Safety Code Section 17958. Fire zone designations and requirements are contained in the California Building Code Chapter 7A and Residential Code Chapter
R337.
On March 24, 2025, the California Department of Forestry and Fire Protection (CAL FIRE) released updated Fire Hazard Severity Zone maps through its Fire and Resource Assessment Program (FRAP), pursuant to Government Code Sections 51175 through 51189. These updated maps are based on advanced modeling of wildfire behavior, including fire propagation through windborne embers. Government Code Section 51179(b)(3) prohibits local jurisdictions from reducing the areas identified by the State.
The updated maps were developed using advanced wildfire behavior modeling through CAL FIRE’s Fire and Resource Assessment Program. The updated methodology incorporates multiple scientific inputs, including historical fire occurrence, projected fire frequency, topography, slope, wind patterns, vegetation type and condition, and climate data. The resulting models simulate the likelihood and intensity of wildfire exposure to determine relative hazard levels across the landscape. These refinements allow for a more geographically precise identification of Very High Fire Hazard Severity Zones (VHFHSZs), particularly in areas susceptible to ember-driven ignition.1 A side-by-side comparison of the pre-3/24/25 and the updated Fire Hazard Severity Zone maps is provided below:
Key changes to the VHFHSZ boundaries in Diamond Bar are as follows:
• Expansion in the Summitridge trail area: Areas east of Diamond Bar Boulevard and north of Grand Avenue surrounding the Summitridge open space area have been upgraded from Moderate or High to Very High Fire Hazard Severity Zones. 1 CAL FIRE. Fire Hazard Severity Zones – Technical Methodology. Fire and Resource Assessment Program (FRAP), 2022. Available at: https://osfm.fire.ca.gov/media/rs4bpmpb/fhsz-tech-methodology2022.pdf • Expansion to the San Bernardino County Line: New VHFHSZ designations now include the neighborhood south of Grand Avenue at the eastern City limits, as well as all of the parcels in The Country east of Derringer and Indian Creek. • Expansion in the south: The Starshine Park and Ronald Reagan Park neighborhoods and other areas adjacent to Pathfinder Road have also been added to the VHFHSZ due to increased modeled fire risk.
• Retraction near Diamond Bar Boulevard: In the central portion of the City, the VHFHSZ boundary has been pulled back from certain developed areas along Diamond Bar Boulevard, reflecting lower hazard conditions. • Minor adjustments elsewhere: Small boundary shifts appear throughout central and southeastern Diamond Bar, with no major reductions observed. • Overall trend: The updated mapping reflects a net increase in areas designated as Very High Fire Hazard Severity Zone, based on improved fire behavior modeling.
In accordance with Government Code Section 51182, CAL FIRE is also required to develop guidance for enforcing defensible space requirements in Very High Fire Hazard Severity Zones (VHFHSZs). These areas are organized into three brush clearance zones, with new regulations for Zones 1 and 2 effective January 1, 2025. Rulemaking for Zone 0 is currently underway.
Brush Clearance Zones
• Zone 0 – Ember-Resistant Zone: No branches, mulch, combustible materials, fencing, or garbage containers within 5 feet of any structure. • Zone 1 – Lean, Clean, and Green Zone: Remove dead plants and branches; maintain at least 10 feet of clearance between tree canopies; manage vegetation between 5 and 30 feet of any structure.
• Zone 2 – Reduced Fuel Zone: Clear combustible shrubs, grasses, debris, and other flammable materials from 30 to 100 feet of any structure.
ANALYSIS:
The proposed ordinance amends Division 12 of Title 15 of the Diamond Bar Municipal Code, which currently references a fire hazard severity zone map dated February 2011, located in Section 15.00.3220(4). That section amends California Residential Code Section R337.2.
The updated ordinance will replace the existing reference with the latest map issued by the State Fire Marshal on March 24, 2025. While the underlying Building and Residential Code requirements remain unchanged, the revised map expands the VHFHSZ to include additional areas, particularly in the northeastern and western portions of the City.
Properties included within the VHFHSZ will be subject to wildfire hardening and brush clearance measures, which include the following construction and defensible space standards:
BUILDING FEATURE REQUIREMENT
Roofing:
Roof Covering Class A
Gaps at Roof Covering Firestopped or No.72 ASTM cap sheet Valleys 26-gauge flashing over 36” wide No.72 ASTM cap
sheet
Gutters Gutter guard/cover
Attic Ventilation:
Screening Fire Marshal/ASTM E2886 listed
Dormer Vent 1/16” to 1/8” noncombustible
Eaves Protected underside
Exterior Wall:
Wall Noncombustible or fire rated materials
Glazing 20-minute or tempered
Doors 1-3/8” thick noncombustible or solid-core
Decking:
Exterior patios, decks,
etc. Noncombustible, heavy-timber, or equal
Brush Clearing:
Defensible Space Vegetation management within 100’ of structure Retrofit Triggers and City Enforcement Role:
While the updated ordinance does not impose retrofit requirements on existing structures, certain wildfire hardening measures are triggered when improvements are proposed. Under California Building Code Chapter 7A and California Residential Code Chapter R337, the following thresholds apply:
• Partial Improvements: When specific building components—such as roofing, attic ventilation, exterior walls, decking, or glazing—are replaced or modified, those elements must comply with current wildfire-resistant construction standards, even if the remainder of the structure remains unchanged.
• Major Alterations: If more than 50 percent of the total roof area is replaced within any 12-month period, the entire roof must be upgraded to a Class A fire-resistant system in accordance with CBC Section 705A. Additionally, any vent, wall, or eave work within the project scope must meet Chapter 7A standards. • New Construction and Substantial Remodels: All new buildings, additions, and substantial remodels located within the VHFHSZ must comply fully with Chapter 7A and R337 requirements for exterior wildfire exposure.
Defensible space and vegetation management requirements, including those for Zones 1 and 2, remain applicable to existing structures pursuant to Public Resources Code Section 4291 and Title 14, Section 1299.03 of the California Code of Regulations, regardless of construction activity.
With respect to Zone 0, which designates the first five feet around a structure as an ember-resistant zone, CAL FIRE has initiated rulemaking as directed by Assembly Bill 3074 (2020). While final regulations and implementation timelines are still pending, local jurisdictions are anticipated to play a key role in enforcement. Once adopted, Zone 0 requirements will supplement existing brush clearance standards by prohibiting combustible vegetation and materials within five feet of any structure in the VHFHSZ.
The City of Diamond Bar may be responsible for implementing these new provisions through building inspections, code enforcement, public education, and coordination with CAL FIRE. Staff will monitor regulatory developments and return to the City Council with proposed amendments or program recommendations as needed to support Zone 0 compliance and wildfire resilience.
ENVIRONMENTAL REVIEW:
The proposed ordinance does not constitute a project under the California Environmental Quality Act (CEQA), as defined by CEQA Guidelines Section 15378(b).
Accordingly, the adoption is exempt from CEQA.
LEGAL REVIEW:
The City Attorney has reviewed and approved the Ordinance as to form.
NOTICE OF PUBLIC HEARING:
In compliance with Government Code Section 50022.3, a Notice of Public Hearing will be published in the San Gabriel Valley Tribune at least 10 days prior to the scheduled hearing on August 5, 2025.
PREPARED BY:
REVIEWED BY:
Attachments:
1. 7.1.a Ordinance No. 02 (2025) - 2025 Fire Zone Map Updates
2. 7.1.b Diamond Bar Fire Hazard Severity Zones, updated 3/24/25